Focus indicating and adjusting device



United States Patent Ofice 3,356,854 Patented Dec. 5, 1967 ABSTRACT 0F THE, DISCLOSURE .iA simple focos-indicating device incorporating a plurality of light paths extendingfrom a desiredfocal plane m an optical device, such as a camera, to a conversion location whereat signals are produced indicating the inf tensrty of transmitted light. A focused image has a larger4 variation between light and dark areas than a defocused image; this is employed herein to produce a variation in signal amplitude for different conditions of focus. The light paths may be divided into groups to thus derive more than one output signal that are compared to each other to produce a difference signal containing no background signals. The light paths may be moved as by oscillation to maximize signal output.

The invention is also adapted for automatic focus adjustment, as by means of a'signal polarity determination and driving means, such as a servo, motor, for lens adjustment to optimum focus.

The present invention relates to devices for indicating when an optical image developed by a camera, range finder, or tlie like, is in best focas, or for automatically adjusting the focus in accordance with the focus indicating signal. t

Devices are known which are capable of developing an observable signal, or the like, which is indicative of the best focus of .an optical image. Such devices have been extensively employed with cameras, range finders, and

other optical instruments, to indicate when the instrumentV is in focus, or in some-instances, to automatically adjust the focus in accordance with tb'e signal. However, previous devices of the foregoing 'pe have usually been relatively complex ard delicate, andin most instances, some vfocus of the image.

in accordance with the general aspects of the invention,

` there is provided an array of optical light paths extending from a common focal image viewing plane to one or more terminal locations. Provision is made to cyclicaily expose `a sample, or a plurality of samples of the light paths at the viewing plane to various difieren: areas of an image, as by vibrating the focal plane terminations of the light paths relative to the image. Preferably, the light paths are in a random array in order to uniformly distribute the light received from an image over the cross section of light paths at the terminal location and thereby eliminate distinctly light and-dark areas therefrom. The light from a defocused blurred image is gray wth respect lo dark and light, there being no shxrp definition between d ark arid light areas of the image. Thus, there are substantially no variations in the intensities of different areas. of the defocused image cyclically received by various of the light path samples, and, accordingly, there is little variation in the intensity of light transmitted `from the terminal location. (lonversely, the light from afocused image has sharp definition between light and dark areas thereof. The ovcr all intensity of light emanating from the terminal location due to the light path samples cyclically viewing various combinations of distinctly light and dark areas of the "focused image varies between relatively high and low values. At one point of the cycle, more samples view dark areas of the image than lig.t areas thereof whereas at l second point o f the cycle more light areas are viewed than dark areas. This, of course, eti'ects a cyclic variation be tween relatively low and high `intensities of the light trans mitted from the terminal location. The magnitude of the variation, or difference between the lcw and high intensities, moreover, increases with the sharpness offocus of the viewed image such that a maximum magnitude or dlference occursin response to mst focus of the image. The invention further includes rnea'ns viewing the light transmitted from the terminal location and indicating the magnitude of the intensity variation as a representation of the focus of an image viewed by the light paths.

In accordance with the foregoing basicconcept, a pre-r ferred embodiment of the invention includes a random array of light paths which are substantially equally divided between a pairof terminal locations. The light -paths are advantageously simply and rnggediy comprised of a ranom bundle of optical bers adapted at one end to view an optical image and bifurcated at the other end to define tvvo 'groups of fibers of substantially equal number. With such an arrangement having two terminal locations, the dilerencebetween the intensities of light transmitted from the respective terminal locations provides a focus indicating signal which is free of extraneous background inten sity variations. More particularly, the focus indicating in tensity variations of light transmitted from the terminal l0- cations of the light pathsarlsing from the cyclic scanning of the image are normally superimposed upon relatively larger order variations in the intensityy of background light;- for example the normal 60 cycle variation ofthe light produced by electrical lighting appliances. Accordingly,`in the provision of a usable focus indicating signal it is desirable that the background intensity variation be removed. The background intensity variation is substantially cancelled in a signal which is proportional to the difference between the 'intensities of'light transmitted from the respective terminal locations because the background light all'ects the paths terminating at the respective terminal locations sub- I stantially equally. It is particularly important to note, howV i ever', that the focus indicating intensity variations are not cancelled in the difference signal. The light paths extending from the viewing plane have a statistically equal probability distribution between the terminal locations. There is equal probability that a given sample-of adjacent light paths are evenly distributed between the two terminal locations; however, in a statistical distribution of equal probability, there is an associated error deviation from an exactly even split in the distribution. As a result, a greater number of light paths of any given sample terminato at one location than the other. There is, accordinalv, a difference between the intensities of light transmitted from the respective terminal locations which varies in accordance with the focus oi the image. The difference signal derived from the pair of terminal locations is thus indicative of the focus of the image. As a further feature of the instant embod'mcnt o the invention, it is to be noted that usually the optical paths at the viewing plane need not be moved relative to the image to provide a focus indicating signal. This feature accrues from the error deviation of a statistically equal probability distribution from an exactly even split between the terminal locations, as will be described in grter deta below.

The invention also provides a modified form of focus indicating device of the type outiined hereinbefore which is. arranged to provide a focus indicating signal proportional to the difference' between the intensities of light transmitted from a pair of tezminal locations which is t zero when the viewed image is in best focus. The signal .passe's through zero from one polarity to the opposite polarity (e.g., from positive to negative) as the position of an. adjustable lens, or the like, producing the image is varied from a'position on one side of that providing bestl focus to a position on the opposite side thereof. The polarit'y of the signal thus indicates which side of best focus the lens position is on. Such a signal is particularlywell suited to the control of a s'crvo drive system, or the like,

for automatically adjusting the lens to a position ofbest focus.

The invention, together with further advantages and ypossible objects thereof, will be better understood upon consideration of the followingV detailed description of a preferred embodiment thereof with reference to the accompanying drawings, wherein:

FIGURE 1 is a schematic View of a preferred embodiment of a device for generating a signa. indicative ofthe focus of an optical image in accordance with the invention;

FlGURE 2 is a view taken at Eine 2``2 of FIGURE 1 illustrating the cross section of the random bundle of optical fibers employed in the embodiment of FIGURE l;`

FIGURE 3 is a schematic `airing diag-rum of a preferred comparison circuit which may be advantageously employed in the development of a focus indicating signal;

FIGURE 4 is a graphical illustration of signal intensity with respect to lens position as produced by the embodiment of FIGURE 1;

FIGURE 5 is a schematic -vievr of a morlied form of device in accordance with the mention; and

FlGURE 6 is a graphical illustration of signal intensity with respect to lens position as produced by the embodiment of FIGURE 5.

v Considering now the invention in some detail and referring to the illustrated forms thereof in the'drawings, there will be seen to be provided a device for generating a signal representative of the best focus of anV optical image, or for otherwise indicating when an image is in best focus. The device is described hereinafter with par ticular reference to visible images, as produced by cameras, range finders, telescopes, etc. However, it is to be noted.that the device isalso useful in applications involving invisibleemanations in the electromagnetic radiation spectrum, c g., infrared radiation. As noted previously, the invention generally comprises means defining a plurality of optical light paths attending from an image viewing plane to atleast one terminal location, preferably with a statistically `random distribution. The light paths are advantageously defined by a random bundle of optical bers. Means are provided for vibrating or oscillating the light paths along, for example, an e "ptical path in the image viewing plane so as to cyc ly expose different samples of the light pabs to dite-.ent areas of an image. The different samples ef the light paths may, for example, be defined bya percrate opaque mask or grating secured to the light path defining means at the vien-ing plane'in interccpting relation to the light paths. The means for moving the light paths may be various mechanical, electromechanical. or equivalent devices operazively associated with the iighz'path d g nteans, or hand movementof thelight path dening ans may be employed for this purpose'. There are urrer provided means foi viewing the light transmitted from the light paths :it the terminal location thereof and providing a light intensity variation signal es an indication of the focus of an image. The signal may, for example, be pro. portional to the difference between the maximum and minimum levels of the cyclic light intensity variation effected in response to movement of the light paths in the viewing plane relative to the image. When the image is blurred or defocused, there is yery little definition between dark and light areas thereof and same may be termed gray. As the various samples of the light paths are swept over different areas of the image, there is consequently only a slight variation in intensity, and a signal proportional to the difference between the maximum and minimum levels of variation of light transmitted from the terminal location is relatively small. Of course, as

'the image approaches best focus. Bcst focus is consequently indicated by a maximum derence'signal. The

means for Vviewing the light transmitted from the terminal location and-providing a focus indicating signal may include, for example, a photoceli or equivalent means for generating an electrical signal proportional to the intensity of .light incident thereon. .An AC volltneler, for example, may then'be employed to indicate the magnitude of the cyclic variation of the electrical signal and therefore the focus o the viewed image. As previously noted, the indicating signal is normally superimposed upon a background signal arising from background light and in some instances the background signal may undergo relatively large variations compared to those of the indicating signal. This is particularly the case in an indoor environment wherein there is a substantial cycle varia tion in the background light duc to the use of 60 cycle lighting appliances. Under these circumstances, the variation of the focus indicating signal is substantially undescernible by virtue of the much larger variation in the background signal intensity. Accordingly, the focus indi eating device of the present invention preferably includes means for eliminating background signal variations. For example, a 60 cycle lten'ng network might be employed to eliminate the undesirable 60 cycle background com poncnt from the electrical signal applied to the voltmeter, or the like. More preferably. however, the light paths of the device are divided between at least one pair of terroinal locations and a signal proportional to the difference between the intensities of light transmitted from the re spective terminal lccations is derived as the focus indieating signal. Background variations in light intensity are thereby cancelled out. A preferred embodiment of the invention in accordance with this conceptis described in detail below.

Referring to FlGURE 1, a preferred embodiment of the focus indicating means includes a plurality of optical light paths which extend from a common vmage viewing plane, as generallyv indicated at 11, to a plurality of terminal locations 12. The plane 11 may be, for example, the focal plane or' an adjustable lens 13 of a camera, or

D other optical instrument. The light paths are substantially transversely across this end of the bundle. The nzask perforations define a number of samples ofthe fibers exposed therethrough to the image at the focal plane 11. The other end of the bundle is bifurcated to provide two groups 17 and 17' of substantially equal numbers of the fibers 14 extending to the terminal locations 12 and 12'. In addition, means are preferably provided to oscillate or vibrate the bundle 15 along, for example, an elliptical path in the focal plane 11 in ordcrto cyclically expose the respev tive samples of fibers defined by the mask perforations to different areas of an image atthe focal plane. Such vibration means are generally indicated at 18, and the dashed line 19 indicates operative association with the bundle.

` It will be appreciated that by virtue of therandom distribution of the fibers 14 of the bundle 15, there is a statistically even probability that adjacent fibers of a given sample respectively terminate at separate locations 12 and 12'. ln such a statistical distribution, however, it

distributed between two terminar' locations such as locations 12 and 12', for any given sample of n paths,

. Ei 2 paths,` terminate at one location, while -tween the light intensities at the terminal locations is will be appreciated that there is an error deviation from. 1?

an exactly even split betweenthe terminal locations. From' the laws of statistical probability, of any given sample ofA fibers, a larger number will most likely terminate at one location than at the other because of the error deviation *from an exactly even distribution. As a result, for any given position of the samples with respect to a sharply focused image at the plane 11, there will be a substantial difference in the light intensities at the terminal loc-ations 12 and 12 because in any sample of fibers, including a composite of all of the samples of fibers, more fibers un-v der one condition of illumination terminate at one location than the other by virtue of the error deviation in the distribution. Of course, the amount of difference be- V tween the light intensities at the terminal locations 12 and 12' cyclically varies by virtue of the movement of the samples of fibers with respect to the image as affected 0 by the vibration means 17. Any given sharp line or departure between light and dark in an image will be cyclically eirposed to a plurality of samples of the fibers such that in one position of the cycle more samples will be illuminated than are dark, while in another position more samples v ill be dark than are illuminated. There is thus effected a cyclically varying difference between the intensities at the terminal locations. The variations are of rela tively large order where there is sharp definition between light and dark areas of the image as exist when same is image is defocused and substantially gray over all. Moreover, it will be appreciated that background components are cancelled in the difference between the light intensities transmitted from the respective'terminal locations. It is c of further importance to note that by virtue of the error deviation from an exactly even distribution of the fibers between the terminal locations 12 and 12', the instant embodiment is usually operable without requirement of movement of the bundle with respect to the image. The difference between the intensities of light transmitted from the respective Aterminal locations 12 `and 12' varies in accordance with the focus of an image at the focal plane 11 even when the bundle is in xed relation to the image.

Although the statistically distributed light paths in acs co'rdance with the present invention are preferably provided by the optical fiber random bundle 15, as described hereinbefore, it will be appreciatedthat various alternatives are possible in the provision of the light paths. Por example, a plurality of prisms may be suitably arranged and incased in a plastic light transmitter, or the like, to rei-fact light along a piurality o-paths terminating at two or more locations in a statistically distributed manner. An array of mirrors may likewise be employed to reliect light along a plurality of paths in this manner. irrespective of the particular means employed to deliri-e the plu rality of light paths, their statistical distribution is best in accordance with the binomial distribution of probabilities. As a result, for the case of the light paths being proportional to V.; where light and dark areas of the sample exist. It is by virtue of this additive effect between the error deviations that a focus indicating difference signal is produced even when the light paths are not movedor oscillated relative to an image. In instances where more than two teminal locations are employed, appropriate algebraic consideration is given to the error dstribution of the light paths of locations being compared to insure the abovenoted additive effect.

Considering now the means for observing the diference between the light intensities at 4the termina! locations 12 and 12' as an indication of the sharpness of focus of an image at the vfocal plane 11, same will be seen t0 preferably include a pair of photocells 20 and. 26 or equivalent means respectively disposed at the terminal locations 12 and 12' in receiving relation to the light respectively transmitted therefrom. The term photccell," as

employed herein, is to be taken as being'generically indicative of a variety of photosen-sitive devices, including solid-state photo-diodes and phototransistors. The photocells respectively generate electrical signals which are proportional to the intensities of light transmitted from the terminal locations 12 and 12'. It will be appreciated that as an alternative arrangement a single photocell may be employed in conjunction with light chopper means to alternately view the light from the respective terminal locations.l`heelectrical out ut sinal from the single hoto- 1n best focus, and relatively slight variation when the p a p cell is thus pxlsed and successive pulses are alternately proportional .'o the intensities of light from the respective terminal locations. The single photocell arrangement is advantageous from the standpoint of balance, the electrical intensity indicating signals for both ter minal locations being generated by the same device. The electrical output signals of the photocells, or photo-cell, may be applied to comparison means 21 arranged to provide a signal proportional to the difference between the electrical signals thereby generated or to otherwise indicate their difference. Although the comparison means 21 may be variously provided, where two photocells are employed the comparison means is preferably 2rranged as indicated in FIGURE 3. ln this regard, the

negative terminal of, for example, photocell 20 is connected to the positive terminal of photocell 20', while the positive terminal of photocell 20 is connected to the negative terminal of photocell 20' through a balancing resistor 22, Thus, the photoceils are connected in parallel` opposed relationship through the balancing resistor 22.

The variable tap23 of resistor 22 is, in turn, connected through a voltmeter 24, or the like, to the common juncture between the negative terminal and positive terf minal of photocells 20 and 20', respectivelyfln addition, a compensating resistor 26 may be connected across one photocell. in the illustrated case photocell 2u', for the purpose of compensating for differences between the frequency responses of the particular pair of photocells 2t) and 20' employed in the circuit. With the comparison means 1l provided in the manner just described, it lwill .in proportion to the light intensities impingiag same,

and the dierence between signals generated by vthe pl'totocellsl is developed across the voltmeter 24, The

variability of the balancing resistor 22 facilitetesadjust menti of the photocell signals so as to compensate for any inequalities between therespective branches of the system when the focal plane 11 receives light of uniform intensity, i.e., gray light. In other words, the balancing resistor 22 provides a zero calibration adjustment for a completely defocused image at the focal plane 11, the resistor being initially adjusted to' provide azero D.C. voltage indication on the voltmeter 24 in response to the mpingement of gray light uniformly upon the focal plane 11. With the comparison means thus initially calibrated, the reading of the voltrneter 24 may be observed as an indication of the sharpness of focus of an image at the focal plane 11. More particularly, the adjustable lens 13-may be varied until the voltmeter 24 indicates maximum voltage, which voltage is representative of amaximum ditler'ence between the-intensities of ligbt'transumitted from the terminal locations l2 and 12'. In accord ance with the considerations advanced hereinhefore, at

this time there exists maxim-urn sharpness or departure between light and dark areas oi 4samples of adjacent light paths at the focal plane 1l which is indicative of true focus of thc image thereat. Tue variation in signal inten' sity, as recorded by the voltsneter 24, with respect to tlio position of adjustable leas 13 is thus as ndkated in FIG? URE 4, wherein the signal intensity curve exhibits a relatively sharp peak which is centered at the focus position of the lens indicated b v the dashed lise 27. It is believed apparent from the signal intensity curve of FIG- URE 4 that as the position of adjustable lens 13 is varied in either direction away from the focus position 27, the intensity of the signal indicated by voltmezer Ztmpidly drops oit to a negligible vace. At focus of the adjustable lens 13 the signal has a maximum amplitude.

Although the voltmeter 24 is employed in the cornparison circuit of FIGURE 3 to provide an indication of the sharpness of focus of an image produced at the focal plane 11 by the adjustable lens 13, the signal applied to the voltrneter may as Well be employed to control the position ot the lens in such a manner as to automatically focus same. The difference signal developed by the comparison means 21 may; for example, be employed, as indicated in FIGURE l, to control lens adjusting means 28 operatively associated 'with the adjustable lens 13 to vary the position thereof in accordance with the signal. The adjusting means 23 may be, for example, a servo positioning system of a type which is adapted to servo on the peak or maximum of the signal intensity curve of FIG- URE 4. Thus, in response to a low intensity` diierence signal theadjusting means 2S would vary the position of the adjustable lens 13 in the direction or' the focus 27. In response to the maximum intensity o f the signal, variation of the lens position would 'ce terminated and the lens would be thus focused. Accordingly, in the foregoingmanner, the present invention :may be employed for the automatic focusing of a lens.

Considerin now anozher ecflication of toets indicating and adjusting devices in accordance with the invention, it should be noted that eene may be emplmed with a split image range finder. or other split image device, to provide an indicating or co` ci signal representative of whether or not the split ix larly, in the case of the e L viewing plane 11 of the derni): distributed of the device may he disposed in viewing rela focal plane of a split image device. When the imaees are split, the contrast between the split images and u ground is about half of hat it is when the im.;` sA comcide. In addition. the area oi the light paths over which translation of the lens to the the intensities of the split images are distributed is about twice the area over which the intensity of the coinciding images is distributed. As a result, the difference between the intensities of light transmitted from-the terminal locations A12 and 12' is much greater when the images coineideV than when they arc split. Thus, the difference signal developed by the device ofthe present invention is in this case representative of whether or not the split images i coincide,

Referring now to FIGURE 5, there will be seen to be provided a modified form device in accordance with the invention which is arranged to provide a signal intensity versus lens position curve of the type illustrated in FIGURE 6. It is of importance to note that the signal intensity is zero for the best focus position of the lens which is indicated by the dashed line 29. Moreover, the signal intensity curve passes through zero symmetrically from one polarity to the opposite l polarity (e.g., from positive to negative) as the position of the adjustable lens is varied from a position 3l on one side of the best focus position 29 to a 'position 32 on the opposite side thereof. It will be appreciated that the curve ci FIGURE 6 is particularly well suited to the control of a servo system such as may be employed as the adjusting means 28 for varying the position of the adjustable lens 13. ln this regard, the polarity of the signal provides an indication of the direction in which the lens must be varied to obtain best focus. In the illustrated cese, positive polarity indicates that the lens ispositioncd to the right of the best focus position while negative polarity indicares that the lens is positioned to the left of the best focus position. The servo lens adjusting system may thus be arranged to translate the lens to the left in response to a positive signal and to the right in response to a negative signal while retaining the lens position-in response to zero signal. Such. operation may be readily and simply accomplished as byl means of a polarity sensitive Eno motor which rotates in opposite directions, eg., clocrrwise and counterclockwise, in response to positive and negative signas, respectively. -Clockwise rotation may be cmployed to etect translation of the lens to the left, while counterclockwise rotation may be employed to efi'ect right. Thus, when the motor input energization is proportional to the intensity signal, the motor drives the lens in the direction of the best focus position and stops as its input energization becomes zero to thereby position the lens at best focus.

In the provision of a signal intensity curve or' the type depicted in FIGURE 6, the embodiment of FlGURE 5 willbe seen to include randomly distributed light paths which terminate in substantially equal numbers at two planes c-r levels equidistantly disposed on oppcsite sides of the focal plane of a lens. The light paths may be defined by a relatively low density or loosely packed bundle 33 of randomly distributed optical fibers, or equivalent means, wherein substantially half of the fibers 34 terminate at a piane 36 and the other half of the fibers 34' terminate at a plane 36' longitudinally displaced from the plane 36. The low density of the bundle is desired in order that adjacent tibers are relatively widely dispersed so as to freely expose the ends of bers at the interior plane 36" to light transmitted from an image. The bundle is disposed such that thc best focus focal plane 37 of an adjustable lens 3S is positioned centrally between the planes 36 and 36. The bcrs 34 from plane 36 extend in a preferably randomly distributed manner toa first terminal 1ocation 39. while the bers 3-l' from plane 36' ilarly extend inn preferably randomly distributed mrs ner to a second terminal location 39'. Provision is made to vibrate the bundle 33 with respect to an image, and in this regard suitable niccnanic-.tl vibration means may be employed or the bundle muy be vibntted by hand in the manner previously described. lt uill be appreciated tl..t during such UL. ration or movement thc cyclic variation in the intensity of light transmitted from terminal location 39 of focus indicating or adjusting V is greater than that transmitted from terminal locationA 39' when the focus of an image is sharper at plane 36 than it is at plane 36'-, and vice versa; When the sharpness of focus of an image is the same 4as viewed by both planes 36 and 36', the cyclic variations in intensities transmitted from botht'erminal locations 39 and 39' are substantially equal. As the position of the adjustable lens I38' is varied, the position of an adjustable image is longitudinally displaced with respect to the planes 36 and 36. As

t the focused image position is moved in opposite longitudinal directions between the planes 36 and 36', the image' intensity of light transmitted from one terminal location A consequently progressively decreases while that trans# mitted from the other terminal location progressively increases as the position of the focused image is displaced between the planes 36 and 36'. When the position of the Yfocused image is midway between the planes 36 and 36',

Le., at the focal Aplane 37, both planes view equal sharpnesses of vfocus of the image and the variation ot light intensities transmitted from both terminal locations 39 and 39' are thus equal. i

The foregoing may be better understood if it 4is assumed that a focused image is positioned to the left of focal plane 37, and therefore closer to plane 36 than to plane 36'. The image will thus appear to be relativelysharp at plane 36 and relatively blurred at plane 36'. As various samples of the light paths terminated at the respective viewing planes 36 and 36' are swept over different areas of the image by vibration of the bundle 33. the cyclic.

variation in the intensity of light transmitted from temrinal location 39 is greater than that of light transmitted from terminal location 39'..Now if the focused image is positioned to the right of tbe focal plane 37, and therefore closer to plane 36' than to plane 36, plane 36 views a sharper image than plane 36. As a result, the cyclic variation in light intensity transmitted from terminal location 39' now exceeds that transmitted from terminal location 39. As noted previously, the degrees or' focus viewed by both planes 36 and 36 are the same when the image is positioned at the foca plane 37, as are therefore cyclic intensity variations transmitted from both terminal locations 39 and 39'. Hence, the algebraic dtterence between the rectified D.C components of the cyclic intensity variations transmitted from the respective terminal t locations varies from one polarity to the opposite polarity as the position of the focused image is varied by variation of the position ofthe adjustable lens 38. The difference is zero when the focused image is positioned at focal plane 37 and the lens is at its position of best focus. The curve of the D.C. difference between the intensities of light transmitted from terminal iocations 39 and 39' versus position of lens 3S is consequently as illustrated in PIG- URE 6.

In order to provide an electrical signal proportionzlto the difference between the rectied D.C. components of the light variations at 39 and 39 arid which is therefore indicative of the focus of the image, suitable photoelectric conversion and D.C. difierencing means 41 are provided in light receiving relation to the terminal locations 39 and 3,9'. The means 41 may be quite conventional. The signal may be employed in the manner previously described to control 'lens adjusting means associated with the lens 38 and adjust same to its position of best focus.

Although the present invention has been described here inbefore with respect to but several preferred embodiments, it will be appreciated that numerous variations and modifications may be made therein without departing from the true spirit and scope of the invention, and thus it is not intended to limit the invention except by the terms of the following claims.

wherein said What is claimed is: i

l. Focus indicating apparatus comprising means dening at least one light path extending from a focal image viewing pl'ane to a terminal location, means for moving each light path in said viewing plane relative to an image viewed by said viewing plane to cyclcally expose different areas of said image to each light path whereby a cyclic variation in the light intensity transmitted from said ter minal iocation is etected which progressively increases as the image varies from a defocused to a focused condition, and means viewing the intensity variation of light transmitted from said terminal location and `providing an indication of the magnitude of the variation as a representation of the focus of said image.

2. Apparatus according to claim 1, wherein said means viewing the intensity variation of light transmitted from said terminal location includes photoelectric conversion means for generating an electric signal prcportionalto said intensity variation with the magnitude of said signal lbeing indicative of the focus of said image.

.3. Focus iadicating apparatus comprising means defining an array of optical light paths extending from at least one image viewing plane to at least one terminal location, means for cyclically exposing a plurality of samples of said light paths at cach of said viewing planes to different areas of an image thereby viewed, and means viewing the cyclic variation in light intensity transmitted'from each terminal location as an indication of the focus of said image.

4. Focus light paths are in a random array.

5. Focus indicating apparatus comprising means d'efining a random array of light paths extending from an image viewing plane to a terminal location, means for cyclically exposing samples of said light paths to different areas of an image at said viewing plane, and means for converting the intensity of light transmitted from saidA terminal location to a proportional electrical signal the magnitude cf which varies in accordance with the focus of said image.

6. Focus indicating apparatus comprising means defining an array of optical light paths extending from a focal image viewing plane to a plurality of terminal locations in a statistically equal probability distribution, and means viewing the relative intensities of light transmitted from said terminal locations as an indication of the focus of an image viewed by said viewing plane.

7. Focus indicating apparatus comprising means defining a pluralityr of optical` light paths extending from a focus viewing piane in a statistically even probability distribution to a pair of terminal locations whereby there is equal probability within a range of error deviation that adjacent paths at the focus viewing plane respectively terminate at one or the other of the terminal locations, and means at said terminal locations viewing and comparing the intensities of light received from said paths respec tively terminating thereat as an indication of the focus of an object viewed by said focus viewing plane.

Focus indicating apparatus comprising means denmng a brfurcated group of optical light paths extending from a com rnon position of origin at a focal plane to first and second terminal locations with a statistical distribution of probabiiites such that for any given sample of n adjacent paths,

paths terminate at said paths terminate at said second terminal location, and means viewing the dilierence hetwecnthe intensities of iight transmitted from the light paths at said first and second terminal locations as an indication of the focus of indicating apparatus according to'claim 3,

- 11 an image focused at said focal plane, said focus being indicated by a maximum light intensity d'uerence.

9. Focus indicating apparatus according to claim 8, further defined by said dierence viewing means comprisinv a pair of ph'otocells respectiveiy vievnng said tirst and second terminal locations and electrically connected in opposing relationship to thereby generate an electrical output signal proportional to die difference in light intensities transmitted from the paths at said first and second terminal locations. v

10. Focus indicating apparatus comprising a random bundle of optical fibe positioned at one end to view an optical image and bifurcated at tbe other end to define two groups of fibers o substantially equal number, sub stantially all sets of adjacent fibers at the first end of Vsaid bundle being thereby distributed with equal probabilities between said two groups of fibers at the second end of the bundle, and means indicating the difference in light intensites transmitted by vsaid two groups of fibers as an indication of the sharpness of focus of said Hoptical image.

e l1. Focus indicating apparatus according to Claim l0. further defined by means for oscillating the first end of `said bundle of fibers to eliminate the possibility of light transmitted from a glven portion of said image impinging a sample of adjacent titers at the first end of said bundle `terminating in exactly equal numbersin said groups at the v second end of said bundle.

'12. Focus indicating apparatus according to claim 10,

further defined by said difierence indicating means comprsing a pair of photocells respectively disposed in confronting relation to the ends of said groups of fibers, and

'means electrically connecting said photocells in opposed relationship to develop an electrica] output signal proportional to the difference in light intensities transmitted by -said groups of fibers.

13. Focusing indicating apparatus comprising adjust able lens means for variably focusing an object at a focal plane, a random bundle of optical fibers having one end disposed in viewing relation to said focal plane' and bifurcated at the other end to define two groups of fibers of Asubstantially equal number distributed such that of any sample of n adjacent bers at the firs? end of the bundle of these fibers are disposed in one group while of these fibers are disposed in the other group, a pair of photocells respectivelydisposed in light receiving relation to said groups of fibers and electrically connected in opposition to generate an output signal which varies from a minimum to a maximaal as the focus of said adjustable lens means is varied'rorn a defocused to a focused position, and means t'or moving the first end of said bundle of fibers in said focal plane.

14. Focus indicating apparatus according to claim 13, further defined by said photocells being connected with the positive termina! of one to the negative terminal of the second, and a variable balancing resistor having its opposite ends connected te the negative terminal of the first photocell and the' pof.tive terminal of the second photocell, said resistor boing a variable tap with said .output signal being derivable from between said tap and said terminal locations as an indication of the focus of an image viewed by said viewing planes. t

16. Focus indicating apparatus comprising means defining a pair of equal number random arrays of light paths respectively extending from a pair of longitudinally spaced apart image viewing planes to a pair of terminal locations, and means for viewing the D C. difference between rectified intensity variations of light transmitted from said terminal locations in 'response to movement of said pair of light path arrays relative to an, image tu an indication of the focus ofthe irf-age at a focal plane positioned longitudinally centrally between said image viewing planes.

17. Focus indicating apparatus according to claim 16, further defined by said means for viewing the D.C. difference between rectified intensity variations of light trans` milled from said terminal locations including photoelectrie conversion menus for generating an electrical signal proportional to the difference in rectified variations in light intensity, said electrical signal thereby varying from one polarity to the opposite polarity as the focus of said image -is displaced longitudinally between said viewing planes and passinglhrough zero when said image is focused at said focal plane.

18. An automatic focusing apparatus comprising adjustable lens means for producing an optical image having a sharpness of focus which varies as a lfunction oflens position, means dcluing an array of light paths extending from a focal plane viewirgsaid image to a terminal loca. tion, means for'cyclically exposing samples of said light paths at said focal plane to different areas of said image V-whereby a cyclic variation is produced in the intensity of light transmitted t'nm said terminal location with the magnitude of the intensity variation increasing as a direct function of the sharpness of focus of said image, means viewing said terminal location for converting the light intensity variation transmitted therefrom to an electrical signal proportional to the magnitude of said light intensity variation, and lens adjusting means operatively associated with said lens for varying thc position thereof in accordance with said electrical signal. V

'19. Automatic focusing apparatus comprising adjustable lens means for producing an optical image having a sharpness of focus which varies as a function of lens position, means defining an array of optical light paths extending from a focal pinne viewing said image to a plurality of terminal locutions in a statistical equal probability distribution, means viening-said terminal locations and generating a signal proportional to the difference between the intensities of light transmitted therefrom. and lens adjusting means operativeiy asspciated with said lens for varying the position thereof in accordance with said signal.

20. Automatic focusing apparatus comprising adjustable lens means for producing. an optical image having a sharpness of focus which varies as a function of lens position, said lens means having a focus position wherein the sharpness of foc-.tsin a maximum and positions of increasing displacement from the focus position wherein the sharpness of focus is progressively decreased, means defining a plurality of light paths extending from a focal plane in viewingrelation to said image to a pair of terminal locations with a statistical distribution of probabilities such that for any given sample of n adjacent paths,

paths terminate :1t une terminal location while Alf-t 2*2 signals less than said maximum and maintaining'said i ber respectively terminating at said pair of terminal intensities of liglt transmitted therefrom in response t0 y image, and lens adjusting means operatively associated creasing sharpness of focus, and lens adjusting means for ance `m'th said signal, said lens adjusting means being varying the position of said lens in accordance with said4 inactive in response to zero signal. signal, said adjusting means varying said position of said 23. Automatic focusing apparatus according to daim lens in the direction of said focus position in response to 22 serein said means defining said light paths comprises a loosely packed random bundle of optical fibers,lsad

bundle at one end having fibers terminating at two longitudinaily dsplazed levels defining said image viewing 2l; Automatic focusing apparatus according to claim planes. said bundle bifurcat'ed a1 its other end to dene 20, wherein said means defining the light paths comprises two groups of fibers respectively extending from a random bundle of optical bers bifurcated at one end m levels and the ends of which define said terminal locations.' to-defne two groups of fibers o substantially equal num- 24. Automatic focusing apparatus according to claim 23, further defined by vibration means operatively associated with said bundle to vibrate the ends of said ber: in said image viewing planes.

lens in said lfocus position in response to said maximum of said signal.

locations. 22. Automatic focusing apparatus comprising adjustable lens means for producing an optical image having a 15 sharpness of focus at a predetermined focal piane which References Gted l v .varies as a function of lens position, means defining rst and second equal pluralities of light paths respectively UNITED STATES PATENTS extending from a pair of longitudinally spaced apart image 2,831,057 4,/1958 Orghubef 250..;01 x

viewing planes disposed equidistantly on 'opposite sides -20 235:;994 1/1951 Shurclig gg 1 of said focal plane to a pair of terminal locations, means 2,975,385 l 3 /1951 polnier 33....14 viewing said terminal locations and generating a signal 3,035,175 5/1962 Kis el aL 25(3 310 proportional to the difference in rectified variations in the- 4 3,218,909 11/1965 Fain 88-1 movement of the light paths with respect 'to an optical 25 RALPH G NILSON Primary Enum-nen l with said lens for varying the position thereof in aecord M. A. LEAVIIT, Assistant Emmne. 

13. FOCUSING INDICATING APPARATUS COMPRISING ADJUSTABLE LENS MEANS FOR VARIABLY FOCUSING AN OBJECT AT A FOCAL PLANE, A RANDOM BUNDLE OF OPTICAL FIBERS HAVING ONE END DISPOSED IN VIEWING RELATION TO SAID FOCAL PLANE AND BIFURCATED AT THE OTHER END TO DEFINE TWO GROUPS OF FIBERS OF SUBSTANTIALLY EQUAL NUMBER DISTRIBUTED SUCH THAT OF ANY SAMPLE OF N ADAJECENT FIBERS AT THE FIRST END OF THE BUNDLE 